A shift in foraging behaviour of beluga whales Delphinapterus leucas from the threatened Cumberland Sound population may reflect a changing Arctic food web

Cumberland Sound, an inlet on Baffin Island, Nunavut, Canada, is undergoing changes in sea ice cover, which is affecting the marine food web. A small population of beluga whales Delphina pterus leucas inhabits Cumberland Sound year round and this population is currently listed as threatened. Relatively little is known about the foraging behaviour of these belugas, but we expected that food web changes, primarily an increased abundance of capelin in the region, would have an impact on their diet and dive behaviour. We evaluated fatty acids in blubber samples collected from subsistence-hunted belugas in Cumberland Sound from the 1980s to 2010, and analyzed satellite tag information from 7 belugas tagged in 2006 to 2008 to gain a better understanding of their foraging behaviour. There was a change in the fatty acid profile of beluga blubber from the 1980s compared to the 1990s and 2000s. Specific fatty acids indicative of capelin and Arctic cod increased and decreased over time respectively, suggesting an increased consumption of capelin with a reduction in Arctic cod in summer in more recent years. Dive behaviour suggested different foraging tactics across seasons. Shallow short dives occurred in summer, which may indicate foraging on capelin, while deeper longer dives were made in autumn and winter, possibly indicating foraging on deeper prey such as Arctic cod and Greenland halibut. Potentially, autumn and winter are important foraging seasons for belugas, amassing energy reserves as blubber and creating a possible competitive conflict for resource use between belugas and expanding commercial fisheries.